Charged particle beam devices have many uses, such as inspection of semiconductor devices with nanometer scale features. Modern semiconductor technology is highly dependent on an accurate control of the various processes used during the production of integrated circuits. Accordingly, semiconductor wafers are inspected in order to detect problems. Furthermore, a mask or reticle can be subject to inspection in order to make sure that the mask or reticle accurately defines a desired pattern.
The inspection of wafers or masks for defects can include the examination of the whole wafer or mask area. Thus, there is a challenge to inspect a large area at high resolution. Also, it is desirable to perform inspection rapidly so that production throughput is not limited by the inspection process, if possible.
Scanning electron microscopes (SEM) have been used to inspect wafers. The surface of the wafer can be scanned using a finely focused electron beam. When the electron beam irradiates the wafer, secondary electrons and/or backscattered electrons, i.e. signal electrons, are generated and can be detected. A defect at a location on the wafer can be detected, for example, by comparing an intensity signal of the secondary electrons to a reference signal corresponding to the same location on the pattern.
Wafer and mask defect inspection in semiconductor technology benefits from high resolution and fast inspection tools, which may cover full wafer/mask application and/or hot spot inspection. Electron beams can be used to provide high resolution inspection of samples so as to be able to detect small defects. In particular, from the 20 nm node and beyond, the high-resolution potential of electron beam based imaging tools is in demand to detect many defects of interest.
However, because of the decreasing feature size and increasing demands for higher resolutions, scanning the entire surface of the wafer can take a long time. Accordingly, using a single-beam scanning electron microscope (SEM) for wafer inspection may not be ideal, because of throughput limitations. A multi-beam SEM is therefore desirable. For example, multiple beams, or beamlets, may allow for simultaneous inspection at multiple locations on the sample, increasing throughput. However, there can be many technical difficulties encountered when using a multi-beam system that require inventive solutions, such as difficulties with generation, control, and the operation of multiple charged particle beams.